Fuel for fuel cell system

ABSTRACT

The present invention relates to a fuel for a fuel cell system comprising 5 vol. % or more of hydrocarbons based on the whole fuel, and 0.5-20 mass % of oxygenates in terms of an oxygen content based on the whole fuel, wherein the content of hydrocarbon compounds having a carbon number of 4 is 15 vol. % or less, the content of hydrocarbon compounds having a carbon number of 5 is 5 vol. % or more, the content of hydrocarbon compounds having a carbon number of 6 is 10 vol. % or more, the content of hydrocarbon compounds having carbon numbers of 7 and 8 in total is 20 vol. % or more, and the content of hydrocarbon compounds having carbon numbers of 10 or more is 20 vol. % or less.

TECHNICAL FIELD

The present invention relates to a fuel to be used for a fuel cellsystem.

BACKGROUND ART

Recently, with increasing awareness of the critical situation of futureglobal environments, it has been highly expected to develop an energysupply system harmless to the global environments. Especially urgentlyrequired are to reduce CO₂ to prevent global warming and reduce harmfulemissions such as THC (unreacted hydrocarbons in an exhaust gas),NO_(x), PM (particulate matter in an exhaust gas: soot, unburned highboiling point and high molecular weight fuel and lubricating oil).Practical examples of such a system are an automotive power system toreplace a conventional Otto/Diesel engine and a power generation systemto replace thermal power generation.

Hence, a fuel cell, which has high energy efficiency and emits basicallyonly H₂O and CO₂, has been regarded as a most expectative system torespond to social requests. In order to achieve such a system, it isnecessary to develop not only the hardware but also the optimum fuel.

Conventionally, as a fuel for a fuel cell system, hydrogen, methanol,and hydrocarbons have been candidates.

As a fuel for a fuel cell system, hydrogen is advantageous in a pointthat it does not require reformer, however, because of a gas phase at anormal temperature, it has difficulties in storage and loading in avehicle and special facilities are required for its supply. Further, therisk of inflammation is high and therefore, it has to be handledcarefully.

On the other hand, methanol is advantageous in a point that it isrelatively easy to reform, however power generation quantity per weightis low and owing to its toxicity, handling has to be careful. Further,it has a corrosive property, special facilities are required for itsstorage and supply.

Like this, a fuel to sufficiently utilize the performances of a fuelcell system has not yet been developed. Especially, as a fuel for a fuelcell system, the following are required: power generation quantity perweight is high; power generation quantity per CO₂ emission is high; afuel consumption is low in a fuel cell system as a whole; an evaporativegas (evapo-emission) is a little; deterioration of a fuel cell systemcomprising such as a reforming catalyst, a water gas shift reactioncatalyst, a carbon monoxide conversion catalyst, fuel cell stacks andthe like is scarce to keep the initial performances for a long duration;a starting time for the system is short; and storage stability andhandling easiness are excellent.

Incidentally, in a fuel cell system, it is required to keep a fuel and areforming catalyst at a proper temperature, the net power generationquantity of the entire fuel cell system is equivalent to the valuecalculated by subtracting the energy necessary for keeping thetemperature (the energy for keeping balance endothermic heat andexothermic reaction following the preheating energy) from the actualpower generation quantity. Consequently, if the temperature for thereforming is lower, the energy for preheating is low and that istherefore advantageous and further the system starting time isadvantageously shortened. In addition, it is also necessary that theenergy for preheating per fuel weight is low. If the preheating isinsufficient, unreacted hydrocarbon (THC) in an exhaust gas increasesand it results in not only decrease of the power generation quantity perweight but also possibility of becoming causes of air pollution. To sayconversely, when some kind of fuels are reformed by the same reformerand the same temperature it is more advantageous that THC in an exhaustgas is lower and the conversion efficiency to hydrogen is higher.

The present invention, taking such situation into consideration, aims toprovide a fuel suitable for a fuel cell system satisfying theabove-described requirements in good balance.

DISCLOSURE OF THE INVENTION

Inventors of the present invention have extensively investigated tosolve the above-described problems and found that a fuel comprising aspecific amount of oxygenates (oxygen-containing compounds) is suitablefor a fuel cell system.

That is, a fuel for a fuel cell system according to the first aspect ofthe invention comprises;

(1) 5 vol. % or more of hydrocarbons based on the whole fuel, and 0.5-20mass % of oxygenates in terms of an oxygen content based on the wholefuel, wherein the content of hydrocarbon compounds having a carbonnumber of 4 is 15 vol. % or less, the content of hydrocarbon compoundshaving a carbon number of 5 is 5 vol. % or more, the content ofhydrocarbon compounds having a carbon number of 6 is 10 vol. % or more,the content of hydrocarbon compounds having carbon numbers of 7 and 8 intotal is 20 vol. % or more, and the content of hydrocarbon compoundshaving carbon numbers of 10 or more is 20 vol. % or less.

Further, the fuel for a fuel cell system according to the second aspectof the invention comprises;

(2) 5 vol. % or more of hydrocarbons based on the whole fuel, and 0.5-20mass % of oxygenates in terms of an oxygen content based on the wholefuel, wherein the fuel has distillation properties; the initial boilingpoint in distillation of 24° C. or more and 50° C. or less, the 10 vol.% distillation temperature of 35° C. or more and 70° C. or less, the 90vol. % distillation temperature of 100° C. or more and 180° C. or less,and the final boiling point in distillation of 130° C. or more and 210°C. or less.

The fuel for a fuel cell system comprising the specific amount of theoxygenates is preferable to satisfy the following additionalrequirements;

(3) a sulfur content is 50 ppm by mass or less based on the whole fuel;

(4) saturates are 30 vol. % or more based on the whole hydrocarbons;

(5) olefins are 35 vol. % or less based on the whole hydrocarbons;

(6) aromatics are 50 vol. % or less based on the whole hydrocarbons;

(7) a ratio of paraffins in saturates is 60 vol. % or more;

(8) a ratio of branched paraffins in paraffins is 30 vol. % or more;

(9) heat capacity of the fuel is 2.6 kJ/kg ° C. or less at 15° C. and 1atm in liquid phase;

(10) heat of vaporization is 400 kJ/kg or less;

(11) Reid vapor pressure (RVP) is 10 kPa or more and less than 100 kPa;

(12) research octane number (RON, the octane number by research method)is 101.0 or less;

(13) oxidation stability is 240 minutes or longer; and

(14) density is 0.78 g/cm³ or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow chart of a steam reforming type fuel cell systememployed for evaluation of a fuel for a fuel cell system of theinvention.

FIG. 2 is a flow chart of a partial oxidation type fuel cell systememployed for evaluation of a fuel for a fuel cell system of theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the contents of the invention will be described further indetail.

In the present invention, the content of hydrocarbons is required to be5 vol. % or more based on the whole fuel in view of a high powergeneration quantity per weight and a high power generation quantity perCO₂ emission.

In the present invention, the oxygenates mean alcohols having carbonnumbers of 2-4, ethers having carbon numbers of 2-8 and the like. Moreparticularly, the oxygenates include methanol, ethanol, dimethyl ether,methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether, tertiaryamyl methyl ether (TAME), tertiary amyl ethyl ether and the like.

The content of these oxygenates is required to be 0.5 mass % or more interms of an oxygen content based on the whole fuel in view of a low fuelconsumption of a fuel cell system as a whole, a low THC in an exhaustgas, short starting time of a system and the like, and further isrequired to be 20 mass % or below and most preferably 3 mass % or belowtaking into consideration of a balance between a high power generationquantity per weight and a high power generation quantity per CO₂emission.

In the first aspect of the invention, the content of hydrocarboncompounds having the specific carbon atoms is necessary for thefollowing requirements.

The content of hydrocarbon compounds having a carbon number of 4 (V(C₄)) shows the content of hydrocarbon compounds having 4 carbon atomsbased on the whole hydrocarbons and is required to be 15 vol. % or lesssince the evaporative gas (evapo-emission) can be suppressed to low andthe handling property is good in view of inflammability or the like andpreferably 10 vol. % or less and most preferably 5 vol. % or less.

The content of hydrocarbon compounds having a carbon number of 5 (V(C₅)) shows the content of hydrocarbon compounds having 5 carbon atomsbased on the whole hydrocarbons and is required to be 5 vol. % or morein view of a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission, and a low fuel consumption of afuel cell system as a whole and preferably 10 vol. % or more, morepreferably 15 vol. % or more, further more preferably 20 vol. % or more,much further more preferably 25 vol. % or more, and most preferably 30vol. % or more.

The content of hydrocarbon compounds having a carbon number of 6 (V(C₆)) shows the content of hydrocarbon compounds having 6 carbon atomsbased on the whole hydrocarbons and is required to be 10 vol. % or morein view of a high power generation quantity and a low fuel consumptionof a fuel cell system as a whole and preferably 15 vol. % or more, morepreferably 20 vol. % or more, further more preferably 25 vol. % or more,and most preferably 30 vol. % or more.

Further, the content of hydrocarbon compounds having carbon numbers of 7and 8 (V (C₇+C₈)) in total shows the content of hydrocarbon compoundshaving 7 and 8 carbon atoms in total based on the whole hydrocarbons andis required to be 20 vol. % or more because of a high power generationquantity per weight, a high power generation quantity per CO₂ emission,and a low fuel consumption of a fuel cell system as a whole andpreferably 25 vol. % or more, more preferably 35 vol. % or more, andmost preferably 40 vol. % or more.

Further, in the invention, the content of hydrocarbons having carbonnumbers of 10 or more is not particularly restricted, however, becauseof a high power generation quantity per CO₂ emission, a low fuelconsumption of a fuel cell system as a whole, and small deterioration ofa reforming catalyst to maintain initial performances for a longduration, the total amount of hydrocarbon compounds having a carbonnumber of 10 or more (V (C₁₀₊) based on the whole hydrocarbons isrequired to be 20 vol. % or less, preferably 10 vol. % or less, and mostpreferably 5 vol. % or less.

Incidentally, the above-described V (C₄), V (C₅), V (C₆), V (C₇+C₈), andV (C₁₀₊) are values quantitatively measured by the following gaschromatography. That is, these values are measured in conditions:employing capillary columns of methyl silicon for columns; using heliumor nitrogen as a carrier gas; employing a hydrogen ionization detector(FID) as a detector; the column length of 25 to 50 m; the carrier gasflow rate of 0.5 to 1.5 ml/min, the split ratio of (1:50) to (1:250);the injection inlet temperature of 150 to 250° C.; the initial columntemperature of −10 to 10° C.; the final column temperature of 150 to250° C., and the detector temperature of 150 to 250° C.

In the second aspect of the invention, the distillation properties areas follows.

The initial boiling point (initial boiling point 0) of a fuel is 24° C.or higher and 50° C. or lower, preferably 27° C. or higher and morepreferably 30° C. or higher. The 10 vol. % distillation temperature(T₁₀) is 35° C. or higher and 70° C. or lower, preferably 40° C. orhigher and more preferably 45° C. or higher. The 90 vol. % distillationtemperature (T₉₀) is 100° C. or higher and 180° C. or lower andpreferably 170° C. or lower. The final boiling point in distillation is130° C. or higher and 210° C. or lower and preferably 200° C. or lower.

If the initial boiling point (initial boiling point 0) in distillationis low, the fuel is highly inflammable and an evaporative gas (THC) iseasy to be generated and there is a problem to handle the fuel.Similarly regarding to the 10 vol. % distillation temperature (T₁₀), ifit is less than the above-described restricted value, the fuel is highlyinflammable and an evaporative gas (THC) is easy to be generated andthere is a problem to handle the fuel.

On the other hand, the upper limit values of the 90 vol. % distillationtemperature (T₉₀) and the final boiling point in distillation aredetermined in view of a high power generation quantity per weight, ahigh power generation quantity per CO₂ emission, a low fuel consumptionof a fuel cell system as a whole, a low THC in an exhaust gas, shortstarting time of a system, small deterioration of a reforming catalystto retain the initial properties, and the like.

Further, the 30 vol. % distillation temperature (T₃₀), 50 vol. %distillation temperature (T₅₀), and 70 vol. % distillation temperature(T₇₀) of the fuel of the invention are not particularly restricted,however, the 30 vol. % distillation temperature (T₃₀) is preferably 50°C. or higher and 100° C. or lower, the 50 vol. % distillationtemperature (T₅₀) is preferably 60° C. or higher and 120° C. or lower,and the 70 vol. % distillation temperature (T₇₀) is 80° C. or higher and150° C. or lower.

Incidentally, the above-described initial boiling point (initial boilingpoint 0) in distillation, the 10 vol. % distillation temperature (T₁₀),the 30 vol. % distillation temperature (T₃₀), the 50 vol. % distillationtemperature (T₅₀), the 70 vol. % distillation temperature (T₇₀), the 90vol. % distillation temperature (T₉₀), and the final boiling point indistillation are distillation properties measured by JIS K 2254,“Petroleum products-Determination of distillation characteristics”.

Further, the content of sulfur in a fuel of the invention is notparticularly restricted, however, because deterioration of a fuel cellsystem comprising such as a reforming catalyst, a water gas shiftreaction catalyst, a carbon monoxide removal catalyst, fuel cell stacks,and the like can be suppressed to low and the initial performances canbe maintained for a long duration, the content is preferably 50 ppm bymass or less, more preferably 30 ppm by mass or less, further morepreferably 10 ppm by mass or less, much further more preferably 1 ppm bymass or less, and most preferably 0.1 ppm by mass or less.

Here, sulfur means sulfur measured by JIS K 2541, “Crude Oil andPetroleum Products-Determination of sulfur content”, in case of 1 ppm bymass or more and means sulfur measured by ASTM D4045-96, “Standard TestMethod for Sulfur in Petroleum Products by Hydrogenolysis andRateometric Colorimetry” in the case of less than 1 ppm by mass.

In the invention, the respective contents of saturates, olefins andaromatics are not particularly restricted, however, saturates (V (S)),olefins (V (O)) and aromatics (V (Ar)) are preferably 30 vol. % or more,35 vol. % or less, and 50 vol. % or less, respectively based on thewhole hydrocarbons. Hereinafter, these compounds will separately bedescribed.

In view of a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission, a low fuel consumption of a fuelcell system as a whole, small THC in an exhaust gas, and a shortstarting time of the system, V (S) is preferably 30 vol. % or more, morepreferably 40 vol. % or more, further more preferably 50 vol. % or more,much further more preferably 60 vol. % or more, much further morepreferably 70 vol. % or more, much further more preferably 80 vol. % ormore, much further more preferably 90 vol. % or more, and mostpreferably 95 vol. % or more.

In view of a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission, small deterioration of a reformingcatalyst to maintain the initial performances for a long duration, and agood storage stability, V (O) is preferably 35 vol. % or less, morepreferably 25 vol. % or less, further more preferably 20 vol. % or less,much further more preferably 15 vol. % or less, and most preferably 10vol. % or less based on the whole hydrocarbons.

In view of a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission, a low fuel consumption of a fuelcell system as a whole, small THC in an exhaust gas, a short startingtime of the system, and small deterioration of a reforming catalyst tomaintain the initial performances for a long duration, V (Ar) ispreferably 50 vol. % or less, more preferably 45 vol. % or less, furthermore preferably 40 vol. % or less, much further more preferably 35 vol.% or less, much further more preferably 30 vol. % or less, much furthermore preferably 20 vol. % or less, much further more preferably 10 vol.% or less, and most preferably 5 vol. % or less.

Further, it is most preferable to satisfy the above-described preferableranges of sulfur and the above-described preferable ranges for thearomatics since deterioration of a reforming catalyst can be suppressedto low and the initial performances can be maintained for a longduration.

The values of the above-described V (S), V (O), and V (Ar) are allmeasured value according to the fluorescent indicator adsorption methodof JIS K 2536, “Liquid petroleum products-Testing method of components”.

Further, in the invention, the ratio of paraffins in saturates of a fuelis not particularly restricted, however, because of a high H₂ generationquantity, a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission and the like, the ratio ofparaffins in saturates is preferably 60 vol. % or more, more preferably65 vol. % or more, further more preferably 70 vol. % or more, muchfurther more preferably 80 vol. % or more, much further more preferably85 vol. % or more, much further more preferably 90 vol. % or more, andmost preferably 95 vol. % or more.

The above-described saturates and paraffins are values quantitativelymeasured by the gas chromatography method mentioned above.

Further, the ratio of branched paraffins in the above-describedparaffins is not particularly restricted, however, the ratio of branchedparaffins in paraffins is preferably 30 vol. % or more, more preferably50 vol. % or more, and most preferably 70 vol. % or more because of ahigh power generation quantity per weight, a high power generationquantity per CO₂ emission, a low fuel consumption of a fuel cell systemas a whole, small THC in an exhaust gas, and a short starting time ofthe system.

The amounts of the above-described paraffins and branched paraffins arevalues quantitatively measured by the gas chromatography methodmentioned above.

Further, in the invention, the heat capacity of a fuel is notparticularly restricted, however, the heat capacity is preferably 2.6kJ/kg ° C. or less at 15° C. and 1 atm in liquid phase in view of a lowfuel consumption of a fuel cell system as a whole.

Further, in the invention, the heat of vaporization of a fuel is notparticularly restricted, the heat of vaporization is preferably 400kJ/kg or less because of a low fuel consumption of a fuel cell system asa whole.

Those heat capacity and heat of vaporization can be calculated from thecontents of respective components quantitatively measured by theabove-described gas chromatography and the numeric values per unitweight of the respective components disclosed in “Technical DataBook-Petroleum Refining”, Vol. 1, Chap. 1, General Data, Table 1C1.

Further, in the invention, the Reid vapor pressure (RVP) of a fuel isnot particularly restricted, however, it is preferably 10 kPa or more inrelation to the power generation quantity per weight and preferably lessthan 100 kPa in relation to suppression of the amount of an evaporativegas (evapo-emission). It is more preferably 20 kPa or more and less than90 kPa, further more preferably 40 kPa or more and less than 75 kPa, andmost preferably 40 kPa or more and less than 60 kPa. Here, the Reidvapor pressure (RVP) means the vapor pressure (Reid vapor pressure(RVP)) measured by JIS K 2258, “Testing method for Vapor Pressure ofCrude Oil and Products (Reid Method)”.

Further, in the invention, the research octane number (RON, the octanenumber by research method) is not particularly restricted, however, itis preferably 101.0 or less since deterioration of a reforming catalystcan be suppressed to low and the initial performances of a reformingcatalyst can be maintained for a long duration owing to a high powergeneration quantity per weight, a low fuel consumption of a fuel cellsystem as a whole, small THC in an exhaust gas, and a short startingtime of the system. Here, the octane number by research method (RON)means the research method octane number measured by JIS K 2280,“Petroleum products-Fuels-Determination of octane number, cetane numberand calculation of cetane index”.

Further, in the invention, the oxidation stability of a fuel is notparticularly restricted, however, it is preferably 240 minutes or longerin view of storage stability. Here, the oxidation stability is theoxidation stability measured according to JIS K 2287, “Testing Methodfor Oxidation Stability of Gasoline (Induction Period Method)”.

Further, in the invention, the density of a fuel is not particularlyrestricted, however, it is preferably 0.78 g/cm³ or less sincedeterioration of a reforming catalyst can be suppressed to low and theinitial performances of a reforming catalyst can be maintained for along duration owing to small THC in an exhaust gas and a short startingtime of the system. Here, the density means the density measuredaccording to JIS K 2249, “Crude petroleum and petroleumproducts-Determination of density and petroleum measurement tables basedon a reference temperature(15° C.)”.

A production method of the fuel of the invention is not particularlyrestricted. Practical method is, for example, the fuel can be producedby one or more kinds of oxygenates and further by mixing hydrocarbons atneed.

As for hydrocarbons, for example, the hydrocarbons can be prepared byblending one or more following hydrocarbon base materials; light naphthaobtained by the atmospheric distillation of crude oil, heavy naphthaobtained by the atmospheric distillation of crude oil, desulfurizedlight naphtha obtained by desulfurization of light naphtha, desulfurizedheavy naphtha obtained by desulfurization of heavy naphtha, desulfurizedfull-range naphtha B obtained by desulfurization of naphtha fractionobtained by distillation of crude oil, isomerate obtained by convertinglight naphtha into isoparaffins by an isomerization process, alkylateobtained by the addition reaction (alkylation) of low molecule weightolefins to hydrocarbons such as isobutane, desulfurized alkylateobtained by desulfurizing alkylate, low sulfur alkylate produced fromdesulfurized hydrocarbons such as isobutane and desulfurized lowmolecule weight olefins, reformate obtained by catalytic reforming,raffinate which is residue after extraction of aromatics from reformate,light distillate of reformate, middle to heavy distillate of reformate,heavy distillate of reformate, cracked gasoline obtained by catalyticcracking or hydrocracking process, light distillate of cracked gasoline,heavy distillate of cracked gasoline, desulfurized cracked gasolineobtained by desulfurizing cracked gasoline, desulfurized lightdistillate of cracked gasoline obtained by desulfurizing lightdistillate of cracked gasoline, desulfurized heavy distillate of crackedgasoline obtained by desulfurizing heavy distillate of cracked gasoline,a light distillate of “GTL (Gas to Liquids)” obtained by F-T(Fischer-Tropsch) synthesis after cracking natural gas or the like tocarbon monoxide and hydrogen, desulfurized LPG obtained by desulfurizingLPG, and the like. The fuel can also be produced by desulfurizing byhydrotreating or adsorption after mixing one or more types of the abovebase materials.

Among them, preferable materials as the base materials for theproduction of the fuel of the invention are light naphtha, desulfurizedlight naphtha, isomerate, desulfurized alkylates obtained bydesulfurizing alkylates, low sulfur alkylates produced from desulfurizedhydrocarbons such as isobutane and desulfurized low molecule weightolefins, desulfurized light distillate of cracked gasoline obtained bydesulfurizing a light distillate of cracked gasoline, a light distillateof GTL, desulfurized LPG obtained by desulfurizing LPG, and the like.

A fuel for a fuel cell system of the invention may comprise additivessuch as dyes for identification, oxidation inhibitors for improvement ofoxidation stability, metal deactivators, corrosion inhibitors forcorrosion prevention, detergents for keeping cleanness of a fuel system,lubricity improvers for improvement of lubricating property and thelike.

However, since a reforming catalyst is to be scarcely deteriorated andthe initial performances are to be maintained for a long duration, theamount of dyes is preferably 10 ppm or less and more preferably 5 ppm orless. For the same reasons, the amount of oxidation inhibitors ispreferably 300 ppm or less, more preferably 200 ppm or less, furthermore preferably 100 ppm or less, and most preferably 10 ppm or less. Forthe same reasons, the amount of metal deactivators is preferably 50 ppmor less, more preferably 30 ppm or less, further more preferably 10 ppmor less, and most preferably 5 ppm or less. Further, similarly since areforming catalyst is to be scarcely deteriorated and the initialperformances are to be maintained for a long duration, the amount ofcorrosion inhibitors is preferably 50 ppm or less, more preferably 30ppm or less, further more preferably 10 ppm or less, and most preferably5 ppm or less. For the same reasons, the amount of detergents ispreferably 300 ppm or less, more preferably 200 ppm or less, and mostpreferably 100 ppm or less. For the same reasons, the amount oflubricity improvers is preferably 300 ppm or less, more preferably 200ppm or less, and most preferably 100 ppm or less.

A fuel of the invention is to be employed as a fuel for a fuel cellsystem. A fuel cell system mentioned herein comprises a reformer for afuel, a carbon monoxide conversion apparatus, fuel cells and the like,however, a fuel of the invention may be suitable for any fuel cellsystem.

The reformer is an apparatus for obtaining hydrogen, by reforming afuel. Practical examples of the reformer are:

(1) a steam reforming type reformer for obtaining products of mainlyhydrogen by treating a heated and vaporized fuel and steam with acatalyst such as copper, nickel, platinum, ruthenium and the like;

(2) a partial oxidation type reformer for obtaining products of mainlyhydrogen by treating a heated and vaporized fuel and air with or withouta catalyst such as copper, nickel, platinum, ruthenium and the like; and

(3) an auto thermal reforming type reformer for obtaining products ofmainly hydrogen by treating a heated and vaporized fuel, steam and air,which carries out the partial oxidation of (2) in the prior stage andcarries out the steam type reforming of (1) in the posterior stage whileusing the generated heat of the partial oxidation reaction with acatalyst such as copper, nickel, platinum, ruthenium and the like.

The carbon monoxide conversion apparatus is an apparatus for removingcarbon monoxide which is contained in a gas produced by theabove-described reformer and becomes a catalyst poison in a fuel celland practical examples thereof are:

(1) a water gas shift reactor for obtaining carbon dioxide and hydrogenas products from carbon monoxide and steam by reacting a reformed gasand steam in the presence of a catalyst of such as copper, nickel,platinum, ruthenium and the like; and

(2) a preferential oxidation reactor for converting carbon monoxide intocarbon dioxide by reacting a reformed gas and compressed air in thepresence of a catalyst of such as platinum, ruthenium and the like, andthese are used singly or jointly.

As a fuel cell, practical examples are a proton exchange membrane typefuel cell (PEFC), a phosphoric acid type fuel cell (PAFC), a moltencarbonate type fuel cell (MCFC), a solid oxide type fell cell (SOFC) andthe like.

Further, the above-described fuel cell system can be employed for anelectric automobile, a hybrid automobile comprising a conventionalengine and electric power, a portable power source, a dispersion typepower source, a power source for domestic use, a cogeneration system andthe like.

EXAMPLES

The properties of base materials employed for the respective fuels forexamples and comparative examples are shown in Tables 1 and 2.

Also, the properties of the respective fuels employed for examples andcomparative examples are shown in Table 3.

TABLE 1 desulfur- desulfur- light middle to ized full- ized full-distillate heavy range range of distillate naphtha naphtha B reformateof *1 *2 *3 reformate sulfur 0.3 0.3 0.2 0.4 hydrocarbon ratio carbonnumber: C₄ vol. % 1.6 0.2 18.0 0.0 carbon number: C₅ vol. % 12.5 9.549.9 0.0 carbon number: C₆ vol. % 19.7 22.5 31.9 0.6 carbon number: C₇vol. % 20.9 22.3 0.2 36.2 carbon number: C₈ vol. % 24.3 24.4 0.0 47.9carbon number: C₇ + C₈ vol. % 45.2 46.7 0.2 84.1 carbon number: C₉ vol.% 18.5 18.6 0.0 13.3 carbon number: C₁₀₊ vol. % 2.5 2.5 0.0 2.0composition saturates vol. % 92.8 94.4 97.2 4.5 olefins vol. % 0.6 0.81.8 0.1 aromatics vol. % 6.6 4.8 1.1 95.4 paraffins in saturates vol. %85.5 87.3 99.0 98.4 branched paraffins in vol. % 44.4 45.0 62.9 48.4paraffins oxygen mass % 0.0 0.0 0.0 0.0 distillation initial boilingpoint ° C. 35.0 42.0 22.0 102.5 10% point ° C. 55.0 59.5 26.0 117.5 30%point ° C. 73.5 75.5 32.5 123.0 50% point ° C. 91.5 92.0 40.5 129.5 70%point ° C. 112.5 111.5 47.5 137.5 90% point ° C. 134.5 135.0 54.0 151.0final boiling point ° C. 155.5 152.5 66.0 191.5 heat capacity kJ/kg · °C. 2.105 2.113 2.230 1.715 (liquid) heat capacity (gas) kJ/kg · ° C.1.523 1.536 1.586 1.172 heat of vaporization kJ/kg 317.2 324.7 348.1344.4 RVP kPa 66.9 58.6 127.5 7.0 research octane 63.4 60.1 78.2 111.5number oxidation stability min. >1440 >1440 >1440 >1440 density g/cm³0.7085 0.7112 0.6487 0.8621 net heat of kJ/kg 44225 44267 44974 41024combustion cracked desulfurized cracked light cracked gasoline gasolinelight alkylate *5 *6 gasoline *7 *8 sulfur 80 7 0.7 8 hydrocarbon ratiocarbon number: C₄ vol. % 7.3 13.4 13.2 8.6 carbon number: C₅ vol. % 25.147.1 47.0 3.2 carbon number: C₆ vol. % 20.1 29.2 29.9 2.8 carbon number:C₇ vol. % 18.1 8.8 8.7 2.5 carbon number: C₈ vol. % 13.7 1.4 1.2 79.8carbon number: C₇ + C₈ vol. % 31.8 10.2 9.9 82.3 carbon number: C₉ vol.% 11.4 0.0 0.0 1.1 carbon number: C₁₀₊ vol. % 4.3 0.0 0.0 2.0composition saturates vol. % 47.2 45.0 46.5 99.8 olefins vol. % 39.453.7 52.3 0.1 aromatics vol. % 13.4 1.3 1.2 0.1 paraffins in saturatesvol. % 85.6 93.5 94.0 100.0 branched paraffins in vol. % 88.6 86.1 86.391.3 paraffins oxygen mass % 0.0 0.0 0.0 0.0 distillation initialboiling point ° C. 31.5 24.5 24.5 31.0 10% point ° C. 51.5 32.5 31.071.5 30% point ° C. 77.0 38.5 37.5 98.5 50% point ° C. 111.5 45.0 44.5105.5 70% point ° C. 150.5 53.5 53.5 110.0 90% point ° C. 189.0 69.569.0 122.5 final boiling point ° C. 216.5 93.5 92.0 181.5 heat capacity(liquid) kJ/kg · ° C. 2.063 2.159 2.167 2.071 heat capacity (gas) kJ/kg· ° C. 1.464 1.519 1.523 1.590 heat of vaporization kJ/kg 333.2 353.2352.7 289.8 RVP kPa 62.5 115.3 115.8 58.5 research octane 92.3 95.5 95.095.6 number oxidation stability min. 210 150 150 >1440 density g/cm³0.7388 0.6601 0.6590 0.6955 net heat of kJ/kg 43903 44589 44555 44488combustion *1: those obtained by desulfurization of naphtha fractionsobtained by distillation of crude oil *2: those obtained bydesulfurization of naphtha fractions obtained by distillation of crudeoil *3: light components obtained by further distilling reformate *4:middle to heavy components obtained by further distilling reformate *5:gasoline fractions obtained by treating heavy, decreased pressure lightoils and the like with a cracking process *6: light fractions obtainedby distilling cracked gasoline *7: desulfurized light fractions obtainedby distilling cracked gasoline *8: gasoline fractions obtained bytreating butane, butene fractions with an alkylation process

TABLE 2 low sulfur GTL alkylate naphtha desulfurized *9 *10 LPG *11 MTBEsulfur 0.1 0.1 0.4 0.1 hydrocarbon ratio carbon number: C₄ vol. % 8.42.1 98.0 — carbon number: C₅ vol. % 3.3 12.4 0.1 — carbon number: C₆vol. % 2.9 19.7 0.0 — carbon number: C₇ vol. % 2.4 21.0 0.0 — carbonnumber: C₈ vol. % 80.2 23.6 0.0 — carbon number: C₇ + C₈ vol. % 82.644.6 0.0 — carbon number: C₉ vol. % 0.9 17.7 0.0 — carbon number: C₁₀₊vol. % 1.9 3.5 0.0 — composition saturates vol. % 99.7 100.0 99.5 —olefins vol. % 0.2 0.0 0.5 — aromatics vol. % 0.1 0.0 0.0 — paraffins insaturates vol. % 100.0 100.0 100.0 — branched paraffins in vol. % 91.453.5 34.6 — paraffins oxygen mass % 0.0 0.0 0.0 18.2 distillationinitial boiling point ° C. 30.5 31.5 — 55.0 10% point ° C. 71.0 47.5 — —30% point ° C. 99.0 69.5 — — 50% point ° C. 105.0 92.5 — — 70% point °C. 110.5 113.5 — — 90% point ° C. 121.5 129.5 — — final boiling point °C. 177.0 150.5 — — heat capacity kJ/kg · ° C. 2.071 2.167 2.369 2.075heat capacity (gas) kJ/kg · ° C. 1.594 1.590 1.628 1.477 heat ofvaporization kJ/kg 290.8 309.5 379.6 319.7 RVP kPa 59.5 72.3 339.0 53.0research octane 95.4 51.5 95.0 118.0 number oxidation stabilitymin. >1440 >1440 — — density g/cm³ 0.6951 0.6825 0.5776 0.7456 net heatof kJ/kg 44501 44576 45689 35171 combustion ethanol methanol DME *12sulfur 0.1 0.1 0.1 hydrocarbon ratio carbon number: C₄ vol. % — — —carbon number: C₅ vol. % — — — carbon number: C₆ vol. % — — — carbonnumber: C₇ vol. % — — — carbon number: C₈ vol. % — — — carbon number:C₇ + C₈ vol. % — — — carbon number: C₉ vol. % — — — carbon number: C₁₀₊vol. % — — — composition saturates vol. % — — — olefins vol. % — — —aromatics vol. % — — — paraffins in saturates vol. % — — — branchedparaffins in vol. % — — — paraffins oxygen mass % 34.8 49.9 34.8distillation initial boiling point ° C. 78.0 64.7 −25.0 10% point ° C. —— — 30% point ° C. — — — 50% point ° C. — — — 70% point ° C. — — — 90%point ° C. — — — final boiling point ° C. — — — heat capacity (liquid)kJ/kg · ° C. 2.339 2.456 2.510 heat capacity (gas) kJ/kg · ° C. 1.3811.343 1.389 heat of vaporization kJ/kg 855.6 1096.8 467.8 RVP kPa 15.930.0 843.2 research octane 130.0 110.0 — number oxidation stability min.— — density g/cm³ 0.7963 0.7961 0.6709 net heat of kJ/kg 26824 1991628840 combustion *9: gasoline fractions obtained by treatingdesulfurized butane, butene fractions with an alkylation process *10:“Gas to Liquid” naphtha fractions which are obtained by cracking naturalgas or the like to CO and H₂ and then subjecting to synthesis,decomposition, and isomerization *11: desulfurized LPG fractions *12:dimethyl ether

TABLE 3 Comp. EX. 1 Ex. 2 Ex. 3 EX. 4 Mixing desulfurized LPG 2% ratiodesulfurized full-range naphtha 94% Component desulfurized full-rangenaphtha B GTL naphtha 91% alkylate 20% low sulfur alkylate 20% crackedlight gasoline 30% cracked gasoline desulfurized cracked light gasoline30% light distillate of reformate 3% 3% middle to heavy distillate ofreformate 30% 30% methanol 6% ethanol 9% MTBE 15% 15% DME 2% PropertiesSulfur ppm by mass 0.3 0.1 3.5 0.4 ratio by carbon number carbon number:C₄ vol. % 1.6 2.1 7.6 9.5 carbon number: C₅ vol. % 12.5 12.4 19.6 19.2carbon number: C₆ vol. % 19.7 19.7 12.7 12.6 carbon number: C₇ vol. %20.9 21.0 16.9 16.5 carbon number: C₈ vol. % 24.3 23.6 37.0 36.1 carbonnumber: C₇ + C₈ vol. % 45.2 44.6 53.9 52.7 carbon number: C₉ vol. % 18.517.7 5.1 4.9 carbon number: C₁₀₊ vol. % 2.5 3.5 1.2 1.2 Compositionsaturates vol. % 92.8 100.0 45.4 47.2 olefins vol. % 0.0 0.0 19.5 18.6aromatics vol. % 6.6 0.0 35.1 34.2 paraffins in saturates vol. % 85.5100.0 97.6 97.8 branched paraffins in vol. % 44.4 53.5 85.7 83.2paraffins Oxygen mass % 3.3 3.6 3.4 2.8 Density g/cm³ 0.7138 0.69270.7405 0.7382 Distillation properties initial boiling point ° C. 35.031.0 28.5 29.0 10% point ° C. 51.0 46.5 50.5 50.0 30% point ° C. 65.568.0 67.5 68.0 50% point ° C. 85.0 84.5 89.5 89.0 70% point ° C. 104.0103.0 106.0 105.0 90% point ° C. 129.5 122.0 125.5 125.0 final boilingpoint ° C. 150.0 145.5 160.5 158.0 Reid vapor pressure kPa 80 77 76 77Research octane number 68.9 59.2 99.3 99.5 Oxidation stability min. 1440or 1440 or 1440 or 1440 or more more more more Net heat of combustionkJ/kg 42598 42740 41627 41915 Heat capacity (liquid) kJ/kg · ° C. 2.1282.185 1.983 1.982 Heat capacity (gas) kJ/kg · ° C. 1.511 1.568 1.4041.410 Heat of vaporization kJ/kg 369.3 366.0 335.1 333.4 EX. 5 Comp. Ex.1 Comp. Ex. 2 Mixing desulfurized LPG ratio desulfurized full-rangenaphtha 10% 100% desulfurized full-range naphtha B 95% GTL naphthaalkylate low sulfur alkylate cracked light gasoline cracked gasolinedesulfurized cracked light gasoline light distillate of reformate middleto heavy distillate of reformate methanol 90% ethanol MTBE 5% DMEProperties Sulfur ppm by mass 0.3 0.1 0.3 ratio by carbon number carbonnumber: C₄ vol. % 0.2 1.6 1.6 carbon number: C₅ vol. % 95 12.5 12.5carbon number: C₆ vol. % 22.5 19.7 19.7 carbon number: C₇ vol. % 22.320.9 20.9 carbon number: C₈ vol. % 24.4 24.3 24.3 carbon number: C₇ + C₈vol. % 46.7 45.2 45.2 carbon number: C₉ vol. % 18.6 18.5 18.5 carbonnumber: C₁₀₊ vol. % 2.5 2.5 2.5 Composition saturates vol. % 94.4 92.892.8 olefins vol. % 0.8 0.0 0.6 aromatics vol. % 4.8 6.6 6.6 paraffinsin saturates vol. % 87.3 85.5 85.5 branched paraffins in vol. % 45.044.4 44.4 paraffins Oxygen mass % 1.0 45.4 0.0 Density g/cm³ 0.71290.7873 0.7085 Distillation properties initial boiling point ° C. 41.035.0 35.0 10% point ° C. 57.0 55.0 55.0 30% point ° C. 71.0 64.5 73.550% point ° C. 91.0 65.0 91.5 70% point ° C. 111.0 65.5 112.5 90% point° C. 134.5 72.5 134.5 final boiling point ° C. 152.0 125.5 155.5 Reidvapor pressure kPa 59 — 67 Research octane number 62.8 — 63.4 Oxidationstability min. 1441 or 1440 or 1440 or more more more Net heat ofcombustion kJ/kg 43791 22103 44230 Heat capacity (liquid) kJ/kg · ° C.2.111 2.424 2.105 Heat capacity (gas) kJ/kg · ° C. 1.533 1.359 1.523Heat of vaporization kJ/kg 324.4 1026.7 317.2

These respective fuels were subjected to a fuel cell system evaluationtest, an evaporative gas test, and a storage stability test.

Fuel Cell System Evaluation Test

(1) Steam Reforming

A fuel and water were evaporated by electric heating and led to areformer filled with a noble metal type catalyst and kept at aprescribed temperature by an electric heater to generate a reformed gasenriched with hydrogen.

The temperature of the reformer was adjusted to be the minimumtemperature (the minimum temperature at which no THC was contained in areformed gas) at which reforming was completely carried out in aninitial stage of the test.

Together with steam, a reformed gas was led to a carbon monoxideconversion apparatus (a water gas shift reaction) to convert carbonmonoxide in the reformed gas to carbon dioxide and then the produced gaswas led to a solid polymer type fuel cell to carry out power generation.

A flow chart of a steam reforming type fuel cell system employed for theevaluation was illustrated in FIG. 1.

(2) Partial Oxidation

A fuel is evaporated by electric heating and together with air, theevaporated fuel was led to a reformer filled with a noble metal typecatalyst and kept at a 1100° C. by an electric heater to generate areformed gas enriched with hydrogen.

Together with steam, a reformed gas was led to a carbon monoxideconversion apparatus (a water gas shift reaction) to convert carbonmonoxide in the reformed gas to carbon dioxide and then the produced gaswas led to a solid polymer type fuel cell to carry out power generation.

A flow chart of a partial oxidation type fuel cell system employed forthe evaluation was illustrated in FIG. 2.

(3) Evaluation Method

The amounts of H₂, CO, CO₂ and THC in the reformed gas generated from areformer were measured immediately after starting of the evaluationtest. Similarly, the amounts of H₂, CO, CO₂ and THC in the reformed gasgenerated from a carbon monoxide conversion apparatus were measuredimmediately after starting of the evaluation test.

The power generation quantity, the fuel consumption, and the CO₂ amountemitted out of a fuel cell were measured immediately after starting ofthe evaluation test and 100 hours later from the starting.

The energy (preheating quantities) necessary to heat the respectivefuels to a prescribed reforming temperature were calculated from theheat capacities and the heat of vaporization.

Further, these measured values, calculated values and the heating valuesof respective fuels were employed for calculation of the performancedeterioration ratio of a reforming catalyst (the power generation amountafter 100 hours later from the starting divided by the power generationamount immediately after the starting), the thermal efficiency (thepower generation amount immediately after the starting divided by thenet heat combustion of a fuel), and the preheating energy ratio(preheating energy divided by the power generation amount).

Evaporative Gas Test

A hose for filling a sample was attached to a fuel supply port of a 20liter portable gasoline can and the installation part was completelysealed. While an air venting valve of the can being opened, 5 liter ofeach fuel was loaded. On completion of the loading, the air ventingvalve was closed and the can was left still for 30 minutes. After thecan being kept still, an activated carbon adsorption apparatus wasattached to the air venting valve and the valve was opened. Immediately,10 liter of each fuel was supplied from the fuel supply port. After 5minutes of the fuel supply, while the air releasing valve being openedand kept as it was, the vapor was absorbed in the activated carbon andafter that, the weight increase of the activated carbon was measured.Incidentally, the test was carried out at a constant temperature of 25°C.

Storage Stability Test

A pressure resistant closed container was filled with each fuel andoxygen, heated to 100° C. and while the temperature being kept as itwas, the container was kept still for 24 hours. Evaluation was carriedout according to “Petroleum products—Motor gasoline and aviationfuels—Determination of existent gum” defined as JIS K 2261.

The respective measured values and the calculated values are shown inTable 4.

TABLE 4 EX. 1 EX. 2 EX. 3 EX. 4 Evaluation results Electric powergeneration by steam reforming method (reforming temperature = optimumreforming temperature 1)) Optimum reforming ° C. 620 610 600 600temperature 1) Electric energy kJ/fuel kg initial performance 2900029190 28070 28260 100 hours later 28980 29170 28040 28240 performance100 hours later 0.07% 0.07% 0.11% 0.07% deterioration ratio Thermalefficiency 2) initial performance 68% 68% 67% 67% CO₂ generation kg/fuelkg initial performance 2.983 2.953 3.057 3.075 Energy per CO₂ KJ/CO²-kginitial performance 9722 9885 9182 9190 Preheating energy kJ/fuel kg1307 1322 1176 1184 3) Preheating energy 4.5% 4.5% 4.2% 4.2% ratio 4)Electric power generation by partial oxidation reforming method(reforming temperature 1100° C.) Electric energy kJ/fuel kg initialperformance 14110 14450 12810 12910 100 hours later 14100 14440 1279012900 performance 100 hours later 0.07% 0.07% 0.16% 0.08% deteriorationratio Heat efficiency 2) initial performance 33% 34% 31% 31% CO₂generation kg/fuel kg initial performance 2.985 2.954 3.058 3.074 amountEnergy per CO₂ KJ/CO₂-kg initial performance 4727 4892 4189 4200Preheating energy kJ/fuel kg 2033 2091 1879 1883 3) Preheating energy14.4% 14.5% 14.7% 14.6% ratio 4) Evaporative gas test Evaporative gasg/test 12.8 9.2 11.1 10.7 Storage stability test Washed existent mg/100ml 1 1 2 1 gum 1) the minimum temperature at which no THC is containedin a reformed gas 2) electric energy/net heat of combustion of fuel 3)energy necessary for heating a fuel to a reforming temperature 4)preheating energy/electric energy EX. 5 Comp. Ex. 1 Comp. Ex. 2Evaluation results Electric power generation by steam reforming method(reforming temperature = optimum reforming temperature 1)) Optimumreforming ° C. 630 460 670 temperature 1) Electric energy kJ/fuel kginitial performance 29580 18280 29850 100 hours later 29550 18270 29820performance 100 hours later 0.10% 0.05% 0.10% deterioration ratioThermal efficiency 2) initial performance 68% 83% 68% CO₂ generationkg/fuel kg initial performance 3.067 1.529 3.098 Energy per CO₂KJ/CO²-kg initial performance 9645 11956 9634 Preheating energy kJ/fuelkg 1300 1663 1341 3) Preheating energy 4.4% 9.1% 4.5% ratio 4) Electricpower generation by partial oxidation reforming method (reformingtemperature 1100° C.) Electric energy kJ/fuel kg initial performance14280 10650 14380 100 hours later 14260 10640 14370 performance 100hours later 0.14% 0.09% 0.07% deterioration ratio Heat efficiency 2)initial performance 33% 48% 33% CO₂ generation kg/fuel kg initialperformance 3.069 1.530 3.101 amount Energy per CO₂ KJ/CO₂-kg initialperformance 4653 6961 4637 Preheating energy kJ/fuel kg 2008 2533 19883) Preheating energy 14.1% 23.8% 13.8% ratio 4) Evaporative gas testEvaporative gas g/test 3.7 8.1 7.5 Storage stability test Washedexistent mg/100 ml 1 1 1 gum 1) the minimum temperature at which no THCis contained in a reformed gas 2) electric energy/net heat of combustionof fuel 3) energy necessary for heating a fuel to a reformingtemperature 4) preheating energy/electric energy

INDUSTRIAL APPLICABILITY

As described above, a fuel for a fuel cell system of the inventioncomprising a specific amount of oxygenates has performances with smalldeterioration and can provide high output of electric energy and otherthan that, the fuel can satisfy a variety of performances for a fuelcell system.

1. A fuel for a fuel cell system comprising 5 vol. % or more ofhydrocarbons based on the whole fuel, and 0.5-20 mass % of oxygenates interms of an oxygen content based on the whole fuel, wherein a content ofhydrocarbon compounds having a carbon number of 4 is 15 vol. % or less,a content of hydrocarbon compounds having a carbon number of 5 is 5 vol.% or more, a content of hydrocarbon compounds having a carbon number of6 is 10 vol. % or more, a content of hydrocarbon compounds having carbonnumbers of 7 and 8 in total is 20 vol. % or more, a content ofhydrocarbon compounds having carbon numbers of 10 or more is 20 vol. %or less, a sulfur content is 1 ppm by mass or less based on the wholefuel, saturates are 30 vol. % or more based on the whole hydrocarbons,olefins are 35 vol. % or less based on the whole hydrocarbons, andaromatics are 50 vol. % or less based on the whole hydrocarbons.
 2. Afuel for a fuel cell system according to claim 1, wherein a ratio ofparaffins in saturates is 60 vol. % or more.
 3. A fuel for a fuel cellsystem according to claim 2, wherein a ratio of branched paraffins inparaffins is 30 vol. % or more.
 4. A fuel for a fuel cell systemcomprising 5 vol. % or more of hydrocarbons based on the whole fuel, and0.5-20 mass % of oxygenates in terms of an oxygen content based on thewhole fuel, wherein a content of hydrocarbon compounds having a carbonnumber of 4 is 15 vol. % or less, a content of hydrocarbon compoundshaving a carbon number of 5 is 5 vol. % or more, a content ofhydrocarbon compounds having a carbon number of 6 is 10 vol. % or more,a content of hydrocarbon compounds having carbon numbers of 7 and 8 intotal is 20 vol. % or more, a content of hydrocarbon compounds havingcarbon numbers of 10 or more is 20 vol. % or less, and heat capacity ofthe fuel is 2.6 kJ/kg ° C. or less at 15° C. and 1 atm in liquid phase.5. A fuel for a fuel cell system comprising 5 vol. % or more ofhydrocarbons based on the whole fuel, and 0.5-20 mass % of oxygenates interms of an oxygen content based on the whole fuel, wherein a content ofhydrocarbon compounds having a carbon number of 4 is 15 vol. % or less,a content of hydrocarbon compounds having a carbon number of 5 is 5 vol.% or more, a content of hydrocarbon compounds having a carbon number of6 is 10 vol. % or more, a content of hydrocarbon compounds having carbonnumbers of 7 and 8 in total is 20 vol. % or more, a content ofhydrocarbon compounds having carbon numbers of 10 or more is 20 vol. %or less, and heat of vaporization of the fuel is 400 kJ/kg or less.
 6. Afuel for a fuel cell system comprising 5 vol. % or more of hydrocarbonsbased on the whole fuel, and 0.5-20 mass % of oxygenates in terms of anoxygen content based on the whole fuel, wherein a content of hydrocarboncompounds having a carbon number of 4 is 15 vol. % or less, a content ofhydrocarbon compounds having a carbon number of 5 is 5 vol. % or more, acontent of hydrocarbon compounds having a carbon number of 6 is 10 vol.% or more, a content of hydrocarbon compounds having carbon numbers of 7and 8 in total is 20 vol. % or more, a content of hydrocarbon compoundshaving carbon numbers of 10 or more is 20 vol. % or less, and Reid vaporpressure of the fuel is 10 kPa or more and less than 100 kPa.
 7. A fuelfor a fuel cell system comprising 5 vol. % or more of hydrocarbons basedon the whole fuel, and 0.5-20 mass % of oxygenates in terms of an oxygencontent based on the whole fuel, wherein a content of hydrocarboncompounds having a carbon number of 4 is 15 vol. % or less, a content ofhydrocarbon compounds having a carbon number of 5 is 5 vol. % or more, acontent of hydrocarbon compounds having a carbon number of 6 is 10 vol.% or more, a content of hydrocarbon compounds having carbon numbers of 7and 8 in total is 20 vol. % or more, a content of hydrocarbon compoundshaving carbon numbers of 10 or more is 20 vol. % or less, and researchoctane of the fuel is 101.0 or less.
 8. A fuel for a fuel cell systemcomprising 5 vol. % or more of hydrocarbons based on the whole fuel, and0.5-20 mass % of oxygenates in terms of an oxygen content based on thewhole fuel, wherein a content of hydrocarbon compounds having a carbonnumber of 4 is 15 vol. % or less, a content of hydrocarbon compoundshaving a carbon number of 5 is 5 vol. % or more, a content ofhydrocarbon compounds having a carbon number of 6 is 10 vol. % or more,a content of hydrocarbon compounds having carbon numbers of 7 and 8 intotal is 20 vol. % or more, a content of hydrocarbon compounds havingcarbon numbers of 10 or more is 20 vol. % or less, and oxidationstability of the fuel is 240 minutes or longer.
 9. A fuel for a fuelcell system comprising 5 vol. % or more of hydrocarbons based on thewhole fuel, and 0.5-20 mass % of oxygenates in terms of an oxygencontent based on the whole fuel, wherein a content of hydrocarbon havinga carbon number of 4 is 15 vol. % or less, a content of hydrocarboncompounds having a carbon number of 5 is 5 vol. % or more, a content ofhydrocarbon compounds having a carbon number of 6 is 10 vol. % or more,a content of hydrocarbon compounds having carbon numbers of 7 and 8 intotal is 20 vol. % or more, a content of hydrocarbon compounds havingcarbon numbers of 10 or more is 20 vol. % or less, and density of thefuel is 0.78 g/cm³ or less.
 10. A fuel for a fuel cell system comprising5 vol. % or more of hydrocarbons based on the whole fuel, and 0.5-20mass % of oxygenates in terms of an oxygen content based on the wholefuel, wherein said fuel has distillation properties such that theinitial boiling point in distillation is in the range from 24° C. to 50°C., the 10 vol. % distillation temperature is in the range from 35° C.to 70° C., the 90 vol. % distillation temperature is in the range from100° C. to 180° C., and the final boiling point in distillation is inthe range from 130° C. to 210° C.
 11. A fuel for a fuel cell systemaccording to claim 10, wherein a sulfur content is 50 ppm by mass orless based on the whole fuel.
 12. A fuel for a fuel cell systemaccording to claim 10, wherein saturates are 30 vol. % or more based onthe whole hydrocarbons.
 13. A fuel for a fuel cell system according toclaim 10, wherein olefins are 35 vol. % or less based on the wholehydrocarbons.
 14. A fuel for a fuel cell system according to claim 10,wherein aromatics are 50 vol. % or less based on the whole hydrocarbons.15. A fuel for a fuel cell system according to claim 10, wherein a ratioof paraffins in saturates is 60 vol. % or more.
 16. A fuel for a fuelcell system according to claim 10, wherein a ratio of branched paraffinsin paraffins is 30 vol. % or more.
 17. A fuel for a fuel cell systemaccording to claim 10, wherein heat capacity of the fuel is 2.6 kJ/kg °C. or less at 15° C. and 1 atm in liquid phase.
 18. A fuel for a fuelcell system according to claim 10, wherein heat of vaporization of thefuel is 400 kJ/kg or less.
 19. A fuel for a fuel cell system accordingto claim 10, wherein Reid vapor pressure of the fuel is 10 kPa or moreand less than 100 kPa.
 20. A fuel for a fuel cell system according toclaim 10, wherein research octane number of the fuel is 101.0 or less.21. A fuel for a fuel cell system according to claim 10, whereinoxidation stability of the fuel is 240 minutes or longer.
 22. A fuel fora fuel cell system according to claim 10, wherein density of the fuel is0.78 g/cm³ or less.